Chapter 14 - NAT

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Address Space Management

Scaling the Networkwith NAT and PAT

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Translating Inside Source Addresses

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Port Address Translation

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Establishes static translation between an inside local address and aninside global address

RouterX(config)# ip nat inside source static local-ip global-ip

Marks the interface as connected to the inside

RouterX(config-if)# ip nat inside

Marks the interface as connected to the outside

RouterX(config-if)# ip nat outside

Displays active translations

RouterX# show ip nat translations

Configuring and Verifying StaticTranslation

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Enabling Static NATAddress Mapping Example


Pro Inside global Inside local Outside local Outside global

--- 192.168.1.2 10.1.1.2 --- ---

interface s0ip address 192.168.1.1 255.255.255.0ip nat outside!interface e0ip address 10.1.1.1 255.255.255.0ip nat inside

!ip nat inside source static 10.1.1.2 192.168.1.2

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Establishes dynamic source translation, specifying the ACL that wasdefined in the previous step

RouterX(config)# ip nat inside source list

access-list-number pool name

Defines a pool of global addresses to be allocated as needed

RouterX(config)# ip nat pool name start-ip end-ip

{netmask netmask | prefix-length prefix-length}

Defines a standard IP ACL permitting those inside local addressesthat are to be translated

RouterX(config)# access-list access-list-number permit

source [source-wildcard ]



Configuring and Verifying DynamicTranslation

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Dynamic Address Translation Example


Pro Inside global Inside local Outside local Outside global

--- 171.69.233.209 192.168.1.100 --- ---

--- 171.69.233.210 192.168.1.101 --- ---

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Overloading an Inside Global Address

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Configuring Overloading

Establishes dynamic source translation, specifying the ACL that wasdefined in the previous step

RouterX(config)# ip nat inside source list

access-list-number interface interface overload

Defines a standard IP ACL that will permit the inside local addressesthat are to be translated

RouterX(config)# access-list access-list-number permit

source source-wildcard



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Overloading an Inside Global AddressExample

RouterX# show ip nat translations Pro Inside global Inside local Outside local Outside globalTCP 172.17.38.1:1050 192.168.3.7:1050 10.1.1.1:23 10.1.1.1:23

TCP 172.17.38.1:1776 192.168.4.12:1776 10.2.2.2:25 10.2.2.2:25

hostname RouterX!interface Ethernet0ip address 192.168.3.1 255.255.255.0

ip nat inside!interface Ethernet1ip address 192.168.4.1 255.255.255.0ip nat inside!interface Serial0description To ISPip address 172.17.38.1 255.255.255.0ip nat outside!ip nat inside source list 1 interface Serial0 overload!ip route 0.0.0.0 0.0.0.0 Serial0!access-list 1 permit 192.168.3.0 0.0.0.255access-list 1 permit 192.168.4.0 0.0.0.255!

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Clears a simple dynamic translation entry that contains an insidetranslation or both an inside and outside translation

RouterX# clear ip nat translation inside global-ip

local-ip [outside local-ip global-ip ]

Clears all dynamic address translation entries

RouterX# clear ip nat translation *

Clears a simple dynamic translation entry that contains an outside

translation

RouterX# clear ip nat translation outside

local-ip global-ip

Clears an extended dynamic translation entry (PAT entry)

RouterX# clear ip nat translation protocol inside global-ip

global-port local-ip local-port [outside local-ip

local-port global-ip global-port]

Clearing the NAT Translation Table

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RouterX# show ip nat statistics

Total active translations: 1 (1 static, 0 dynamic; 0 extended)Outside interfaces:

Ethernet0, Serial2

Inside interfaces:

Ethernet1

Hits: 5 Misses: 0

…

Displaying Information with show anddebug Commands

RouterX# debug ip nat

NAT: s=192.168.1.95->172.31.233.209, d=172.31.2.132 [6825]

NAT: s=172.31.2.132, d=172.31.233.209->192.168.1.95 [21852]

NAT: s=192.168.1.95->172.31.233.209, d=172.31.1.161 [6826]

NAT*: s=172.31.1.161, d=172.31.233.209->192.168.1.95 [23311]

NAT*: s=192.168.1.95->172.31.233.209, d=172.31.1.161 [6827]

NAT*: s=192.168.1.95->172.31.233.209, d=172.31.1.161 [6828] NAT*: s=172.31.1.161, d=172.31.233.209->192.168.1.95 [23312]

NAT*: s=172.31.1.161, d=172.31.233.209->192.168.1.95 [23313]

Chapter 14 - NAT

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